Attempt to fix SparkListenerSuite breakage

Could not reproduce locally, but this test could've been flaky if the
build machine was too fast.
Merge pull request #145 from aarondav/sls-fix

Attempt to fix SparkListenerSuite breakage

Could not reproduce locally, but this test could've been flaky if the build machine was too fast, due to typo. (index 0 is intentionally slowed down to ensure total time is >= 1 ms)

This should be merged into branch-0.8 as well.